1. Field of the Invention
The invention relates generally to wear resistant coatings, and more particularly, to a hybrid coating structure for molds and a method for making the same.
2. Description of Related Art
Coatings are commonly formed on a surface of objects, such as molds, thin films and recording discs, etc. The coatings function to protect the underlying layer from damage and wear caused by repeated use. For example, diamond-like carbon (DLC) coatings are conventionally used to protect molds as an overcoat to improve the wear resistance of the molds. The diamond-like carbon coating provides a smooth surface for the molds and minimizes friction of the surface.
Methods for producing diamond-like carbon coatings include carbon deposition by sputtering method—typically direct current magnetron sputtering, in which the ionized gases are directed onto the target by magnetic fields generated in a sputtering device. According to this method, a carbon substrate is sputtered onto a target substrate in a low-pressure argon (Ar) atmosphere until a coating of a desired thickness is reached. The resulting diamond-like carbon coating has a predominant amorphous structure with “islands” of diamond-like crystalline grains.
The properties of the diamond-like carbon coating depend on a mixture proportion of the diamond-like crystalline grains and the amorphous structure. The diamond-like crystalline grains can impart hardness to the target substrate. Unfortunately, there are many gaps between the diamond-like crystalline grains. Corrosion particles are likely to enter the gaps and can corrode the diamond-like carbon coatings, eventually resulting in its failure.
Therefore, these coatings have a poor durability, which necessitates their frequent repair and even total renewal. The frequent repair and touch-up of the coatings may affect molding performance and quality. Further, the downtime associated with maintaining the coating significantly affects productivity. Coatings in use today do not perform adequately because of the low wear and corrosion resistance.
What is needed, therefore, is a coating has high degree of wear resistance and corrosion resistance.